1. Field of the Invention
The present invention relates to porous ceramic balls with a hierarchical porous structure, and a method for preparing the same.
2. Description of the Related Art
Porous materials finds a broad spectrum of applications in many fields, including catalysts and catalyst support, filters, separation/permeable membranes, electrodes, absorbents, scaffold, etc. The control of morphology and porosity thereof plays an important role in improving the properties of porous materials. With an ability to effect a great improvement in surface area, porosity, permeability and selectivity, particularly, porous materials in which hierarchical porous structures such as secondary or tertiary porous structures are formed, are expected to be applicable to various newly arising fields of application including drug delivery systems, biosensors, permeable membranes, filters, etc. Many methods have recently been suggested for the synthesis of porous materials which have a hierarchical porous structure.
For the synthesis of three-dimensional porous structures, many methods are known, including a particle leaching method, a gas foaming method, a fiber mesh method, a phase separation method, an emulsion freeze drying method, etc. However, these synthesis methods find it difficult to control pore sizes and are apt to produce structures which are relatively low in surface area and porosity. In addition, the porous materials obtained by conventional methods hold poor interporous open structures, suffering from pore plugging. Recently, rapid prototyping, which is the automatic construction of physical objects with the aid of a computer system, has been suggested for the construction of supports. This technique arises as a solution to the problems of conventional methods and is effective for constructing three-dimensional porous structures which have pore sizes (giant pores: 100-1000 μm) of sufficient size to support the growth of cells.
Conventionally, pore sizes of porous materials are, for the most part, controlled over giant size ranges. In expectation of improvements in cell adhesion, cell proliferation, cell differentiation and prevention of cell necrosis as well as an increase in specific surface area and porosity, control has recently been concentrated on directing the size and morphology of pores, such as double pores (Korean Patent No. 751504) or triple pores (Korean Patent Application No. 2006-103013) within nano, macro, and giant pore ranges. Particularly, studies on the introduction of nano-pores into supports have been conducted in expectation of increasing bioactivity and biodegradability and helping delivery of anticancer and anti-inflammatory agents. Korean Patent Publication No. 2006-105013 describes the synthesis of ceramic supports with giant-, macro-, nano-size pores or ceramic-polymer supports with giant- or nano-size pores using a rapid prototyping or polymer template method, and adds to the significance of structures having multiple pores.
However, the conventional porous ceramic structures show mechanical properties insufficient for use in supports. Although improved in physical strength, the ceramic-polymer supports contain giant- and nano-size pores, but lack macro-size pores which can be used as migration paths for active materials, such as cell nutrients and discharge from cells.
Also, the use of endogenous plates is applied for the construction of self-assembly polymer structures (S. Baral et al., Chem. Mater. 1993. 5. 145), lyotropic liquid crystal structures (C. T. Kresge et al., Nature 1992, 359, 710), mesoporous structures of block copolymers (M. Antonietti et al., Angew. Chem. Int. Ed. 1998. 37. 613), and colloidal arrays (H. P. Nentze et al., Adv. Mater. 1998. 10.154). In addition, construction methods taking advantage of complex morphology based on the topological defects and interfacial defects of inorganic-organic structures (Z. Zhao et al, J. Phys. Chem. B. 1997. 101. 3460) and oil-in-water droplets (F. Schuth et al., Science. 1996. 273. 768), water-in-oil (J. Li et al., Colloids and Surf. A. 2005. 256. 57), and emulsion bubbles (D. J. Pine et al., Nature. 1997. 389. 948) have been suggested.
The G. D. Stucky and M. Takemori group reported a block copolymer template method by which nano- and meso-porous structures with pores ranging from 2 to 50 nm can be constructed (J. Am. Chem. Soc. 1998. 120. 6024; Chem. Mater. 2004. 16. 4181)).
The conventional methods described above are problematic because multi-step processes are required for the methods, and a combination of two or more templates is required for the construction of porous structures having nano-size pores which are limited to two or fewer types.
Leading to the present invention, the application of polymer self-assembly and sol-gel reaction to the formation of porous ceramic balls resulted in the finding that the porous ceramic balls have three-dimensional hierarchical porous structures therein and a large specific surface area and a large porosity, with pores interconnected therebetween, and can be used as bone scaffolds.